Numerous conventional processes require that materials be successively immersed in two or more tanks. Important examples of such processes include the electroplating and chemical treatment of electronic components, such as integrated circuit leadframes and similar components.
In the electronic component industry, discrete or integrated components are typically encapsulated in an electrically insulating material such as a plastic or ceramic package. Metal contacts or leads generally protrude from the package. These contacts or leads often require electroplating or chemical treatment after encapsulation.
It is conventional to accomplish such treatment by loading the parts onto racks or into baskets, and sequentially bathing such racks or baskets into tanks of cleansing and plating solution or the like. It is also conventional to convey the parts along a horizontal path through successive treatment stations using conveyor belts or rails.
For example, U.S. Pat. No. 4,534,843, issued Aug. 13, 1985 to Johnson, et al., discloses an electroplating apparatus having a flexible, electrically conductive conveyor belt that runs in a horizontal loop. Suitable shaped electronic components may be gripped by members attached to the bottom edge of the belt and carried along a horizontal path through successive treatment tanks. Each treatment tank has notches (weirs) at each end, allowing the components to enter and exit the tank but also allowing fluid in the tank to drain out, triggering a need for a means for collecting and recycling the escaping fluid. A complicated loading mechanism is employed to position appropriately sized and oriented components so that they may be gripped by the gripping members. In order to adapt the apparatus to transport differently sized or shaped components, the gripping members must be removed from the belt and replaced by differently sized and shaped gripping members. During electroplating operations, electric current is supplied from a power source through the entire electrically conductive conveyor belt, to the components gripped by the gripping members.
A similar conventional apparatus is disclosed in U.S. Pat. No. 4,508,611, issued Apr. 2, 1985 to Johnson, et al. The apparatus of U.S. Pat. No. 4,506,611 has a vertically oriented, electrically conductive, conveyor belt whose flat surface is oriented horizontally. The belt edges have means by which components may be attached thereto by a loading mechanism. Otherwise, the apparatus of U.S. Pat. Nos. 4,506,611 and that of 4,534,811 are similar. Both require that the treatment tanks be linearly arranged in the same horizontal plane, both require complicated loading mechanisms, and both are energy inefficient because they supply electric current that flows through the entire conveyor belt in order to supply electric current to the components engaged therewith.
Conventional material handling systems, in general, embody all or some of the following disadvantages: complexity, in the sense that extremely accurate positioning mechanisms are required for loading and unloading the components to be conveyed thereby; inability to transport parts having a wide range of shapes and sizes without system modifications; bulky size, occupying large floor areas without realizing the floor space economies attainable by maximizing the use of vertical space above a given floor area; low production rate, because the products to be treated are oriented with their longitudinal axis parallel to their travel path so that few products are processed per unit length of the product travel path; unreliability, in the sense that a percentage of the products being transported, especially delicate products such as electronic components, are damaged during the loading and unloading processes or lost during transportation along the process path; inefficient electric power usage, due to failure to limit the supply of electric power to the process areas only.
Until the present invention, it was not known how to transport materials for treatment at successive treatment stations in a manner eliminating all the mentioned disadvantages.